This invention relates to a method for thermogravimetric analysis of coal due to the formation of volatile matters and ash contents.
When coal is used as a fuel, for example in a fire power plant, it is important to know thermal weight losses due to the formation of volatile matters and ash contents. For this purpose M 8812 in JIS specifies a standard method for thermogravimetric analysis of coal to give information on water, other volatile matters, and ash contents. According to the method in JIS, however, each analysis requires a distinct sample, and inevitably similar measurements have to be repeated; thus complete analysis takes a long time.
The method for thermogravimetric analysis to quantify volatile matters according to M 8812 in JIS, consists of: heating an electric furnace and adjusting temperatures of a specific space for a crucible inside the furnace uniformly to 900.degree. C.; putting a sample (about 1 g) into a platinum crucible with a known weight; putting a lid on the crucible; tapping the bottom of the crucible on a clean, firm plane a few times to make the sample equal in depth inside the crucible; placing the crucible with the lid into the specific space under a nitrogen atmosphere in the uniform temperature in the furnace; heating the crucible under a nitrogen atmosphere in the furnace so that temperatures of the specific space in the furnace reach those in a range of 900.degree..+-.20.degree. C. within three minutes after placing the crucible; keeping the crucible under a nitrogen atmosphere in the furnace for seven minutes after placing the crucible into the specific space; taking the crucible out of the furnace; cooling the crucible on a cold metal plate for a minute; cooling the crucible in a desiccator; and measuring a weight of the crucible with the sample to obtain a relative weight loss of the sample.
The method for thermogravimetric analysis to quantify ash contents according to M 8812 in JIS, consists of: putting a sample (about 1 g) into a crucible with a known weight; placing the crucible into a furnace; heating the crucible under a normal atmosphere to 500.degree. C. in about 60 minutes and then to 815.degree. C. in about an additional 60 minutes or, if necessary, two to three hours; holding the crucible under a normal atmosphere in temperatures ranging from 805.degree. C. to 825.degree. C.; taking the crucible out of the furnace; cooling the crucible in a desiccator for twenty minutes; and measuring a weight of the crucible with the sample to obtain a relative weight loss of the sample.
To overcome the two independent time-consuming procedures, a method has been developed for continuous thermogravimetric analysis out of a single sample of coal. Japanese Patent Laid-Open No. 2-31131 (1990) has disclosed a method for thermogravimetric analysis, comprising: heating a first sample of coal in a crucible without a lid to 950.degree. C. at a heating rate of 110.degree. C. per minute under a nitrogen atmosphere to give a second sample; maintaining the second sample at 950.degree. C. for three minutes to give a third sample; measuring a relative weight loss of the third sample; burning the third sample at 850.degree. C. under an oxygen atmosphere; and measuring a second relative weight loss of the third sample. The values obtained in this method contain systematic errors compared to those obtained in the method in M 8812 in JIS, and, therefore, require corrections.